The Basic Study Of Acromioclavicular Joint Dislocation

Acromioclavicular(AC)joint dislocations account for approximately 9-12% of all shoulder injuries,which may lead to shoulder pain and impairment of shoulder function,thus reducing patients’ quality of life and activity.Many studies have revealed the cosmetic problems and impaired shoulder functions of conservative treatments,and high rates of complications of surgical treatments.Therefore,further studies are needed to improve the clinical results of AC dislocation and to reduce the high rate of complications.This study will be divided into the following two parts,which discuss our improvement of the conservative and surgical treatment of AC dislocation respectively.The first part: To observe the relative displacement between distal clavicle and acromion in intact and injured AC joints with different grades in cadavers,and the influence of shoulder extension to the displacement,to explore a better method for AC joint reduction and maintenance.The second part: To design a new internal fixation equipment which is anatomical,easy and safe to apply and minimally invasive.Then evaluate its clinical value by comparing it with native coracoclavicular(CC)ligaments throughbiomechanical tests.Part 1 The Study of Acromioclavicular Joint Reduction 1 Research Objectives The aim of this study was to observe the relative displacement of injured AC joint with different degrees,and the influence of shoulder extension to the displacement,to explore a better position for AC joint reduction and maintenance.2 Materials And Methods 10 fresh-frozen cadaveric shoulders were used in this study.We simulated Rockwood Ⅱ,Ⅲ and Ⅴ AC joint dislocation models by sequentially sectioning AC ligaments,CC ligaments,and delto-trapezial fascia.In each model,we evaluated the vertical and horizontal distance between distal clavicle and acromion when shoulder extension reached 0°,30°,and 60° in the sagittal plane and 40° oblique sagittal plane.3 Results Acromion displaced anteriorly and inferiorly relative to the distal clavicle in grade Ⅱ,Ⅲ and Ⅴ models and the displacement became larger with the ascending grades.In all grade Ⅱ,Ⅲ and Ⅴ models,the vertical displacement and the horizontal displacement in shoulder extension of 60° was significantly different from that of 0° and 30°in either sagittal plane or 40°oblique sagittal plane.The vertical displacement descended withthe increasing angle of shoulder extension,while the acromion displaced posteriorly with the increasing angle of shoulder extension.Shoulder extension of 60° in sagittal plane showed less horizontal displacement than in 40° oblique sagittal plane,but no significant differences were found in vertical displacement between the two planes.4 Conclusion This study revealed that shoulder extension could reduce the vertical displacement of AC joint dislocation and the vertical displacement was minimal when shoulder extension reached 60°.It also revealed that shoulder extension of 60° in 40° oblique sagittal plane was a good position for Rockwood Ⅱ,Ⅲ and Ⅴ AC joint reduction,which could almost anatomically reduce the AC joint both vertically and horizontally.Part 2 The Biomechanical Study of Coracoclavicular Ligament and A New Internal Fixation Equipment 1 Research ObjectivesDesign a new internal fixation equipment—MSTCS(Multi Strand Titanium Cable Screw),which is anatomical,easy and safe to apply and minimally invasive.Then evaluate its clinical value by comparing it with native CC ligaments through biomechanical tests.2 Materials And Methods 10 fresh-frozen cadaveric shoulders were tested.Cyclic loading and a subsequent load-to failure protocol was performed in vertical directions on CC ligaments and repeated after reconstruction by the MSTCS.3 Results Both CC ligaments and MSTCS survived the cyclic loading protocol.The permanent elongation between CC ligaments(0.31±0.18 mm)and MSTCS(0.32±0.16 mm)were not significantly different.The ultimate loads of native CC ligaments for vertical force measured 459.2±64.9 N,failure elongation 7.6±2.0 mm,and stiffness 63.5±15.1 N/mm;the ultimate loads of MSTCS for vertical force measured 311.2±53.9 N,failure elongation 5.9±1.3mm,and stiffness 54.3±9.0 N/mm.There are significant differences in the ultimate loads and failure elongation,but no difference in stiffness between CC ligaments and MSTCS.4 Conclusion Our study introduced a new internal fixation equipment for AC dislocation,called MSTCS,which is anatomical,easy and safe to apply,and minimally invasive.The in vitro biomechanical test showed that the strength of MSTCS is about 68% of CC ligaments,and overload may lead to screws pulling out.However,MSTCS could survive a physiological load situation in a light postoperative rehabilitation protocol and showed similar elongation characters with CC ligaments,which may help restore the anatomical morphology and function of AC joints and reduce the rate of postoperative subluxation and suture break.